The present invention relates to an evaporator, which performs the cooling of electronic elements and/or electronic equipment, and to a circulation type cooling equipment using the evaporator.
As a semiconductor element used in various electronic equipments malfunctions due to high temperature, it is necessary to control the temperature under a certain level. For this reason, heat radiation is performed by means of heat spreader, heat-sink, fan and the like.
In recent years, it is getting difficult to secure a space where a heat-sink can be provided around the semiconductor element in such small electronic equipment as a note-PC. Therefore, a cooling system including refrigerant and a wick has been a mainstream, which removes the heat generated by the heat element as evaporating latent heat of the refrigerant and transferees it by means of heat pipe to the circumferential area of a casing, where a space for cooling can be easily available.
However, an amount of the transferable heat becomes intensively small as the diameter of the heat pipe becomes smaller. On the other hand, since the electronic equipments are getting more compact in size and higher in their performance, it will be difficult to realize enough cooling by means of heat pipe in future.
Further, in the case of the heat pipe, a flow direction of vapor generated at an evaporating portion and a flow direction of the refrigerant liquefied at a condensing portion, which is returned to the evaporating portion by means of capillarity of the wick are opposite to each other. For this reason, the liquid refrigerant is prevented from flowing in the wick by the vapor (This phenomenon is called as the scattering limit.) due to increases of the amount of the heat or to a decrease of a diameter of the heat pipe. It is another reason for limiting the amount of heat to be transferred that the flow resistance is large due to the wick, through which the refrigerant flows from the condensing portion to the evaporating portion (This phenomenon is called wick limitation.).
The technology that is developed as a replacement of the heat pipe is a Capillary Pumped Loop (hereinafter called as CPL), in which the heat pipe is formed in a loop. In the CPL different from the heat pipe described, there is no scattering limit since the flow direction of the vapor and the flow direction of the liquid returned from the condensing portion to the evaporating portion are coincident. Further, the wick limitation can be made small since there is no need to lay the wick all the way from the condensing portion to the evaporating portion. As the amount of the heat transferred can be made larger than in the heat pipe, this technology is already put into a practical use in the space application. One of such applications is described in Japan Published Unexamined Patent Application 2003-148882.
In the CPL, it is necessary to keep the flow direction of the vapor of the refrigerant in one direction. For this purpose, the Patent Application 2003-148882 proposes a technology to provide a liquid reservoir and hold the refrigerant by a non-return valve which selectively opens and closes depending on the temperature or by a filter.
However, the conventional technology described above are countermeasures against a counter flow of the refrigerant which has really taken place, but are not positive prevention against possible generation of vapor at the evaporating portion, which is a cause of the counter flow of refrigerant. Furthermore, there has been a problem that many materials were necessary to prevent the counter flow.